tonight all of us together are on the verge of making history. Simply by clicking "buy" on the computer screen. The new american tradition, cyber monday, shopping online and what happens in the next few hours could have a big effect on the nation's economy. You can see right here how much. Online shopping on this one day has nearly tripled in the last seven years. Abc's neal karlinsky tells us what we're buying and why the big stores sometimes know even before we do. Reporter: Across the country today, from so-called "couch commerce" at home, to the cubicle at work, americans were buying at a record pace and having every bit of their online behavior tracked. We know that at least half of cyber monday purchases were made from a work computer while the boss wasn't looking, mainly between noon and 2:00 p.M. Browsing reaches a peak in the evening. We know that the most purchase reasonable doubt consumer electronics followed by clothing like jeans and sweatersment and, in a growing trend, we know that more than ever before were doing it on the go from a mobile device, many while walking the aisles inside a store. In fact, an estimated 48 million shoppers now do something called "showrooming," checking out a product or price in the real world before buying it . It's personalized shopping and it's really becoming quite sophisticated. And in a sense it's benefiting the consumer. Reporr: No one has perfected online shopping like amazon, which gave us rare access to 1 of the company's 80 massive fulfillment centers worldwide where we ordered a video game watched it pulled from a shelf by hand, then sent on its way through miles of conveyer belts before being boxed up. Cyber monday is a big deal for us. It's real. It's not something made up so that we can get some hype. Reporter: The company doesn't only sell just about everything, it uses sophisticated programs to track your online habits, a fully customized shopping experience to not only match prices, but increasingly match your desires. I log on and automatic you guys are suggesting I might want this and that. We have teams of super smart people who build algorithms to create personalized recommendations for our customers. Reporter: One thing about online shopping, people return a lot more. Up to 35% of online purchases are returned versus about 18% from traditional stores. As for that video game that i purchased from amazon, it showed up almost before I could get home from phoenix with a note I wrote inside -- happy holidays fc news.

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